1. Field of the Invention
The invention relates to a light emitting diode lamp (herein referred to as an LED lamp) and, particularly, to an LED lamp that a plurality of light emitting elements, and electrode plates and wires for electrical connection with these light emitting elements are housed in a package of a material such as ceramics and are sealed with transparent epoxy resin.
Also, the invention relates to an LED lamp that is intended to have stable solder connectivity when being connected with a wiring pattern.
Herein, an LED chip itself is referred to as a light emitting element or light emitting diode (LED), and a whole structure with a plurality of LED chips is referred to as a light emitting diode lamp or LED lamp.
2. Description of the Related Art
Conventionally, SMD package type LED lamps are used as backlight light source. The SMD package type LED lamp is composed of: a package of synthetic resin formed by injection molding; a plurality of metal leads formed within the package; a plurality of LED's mounted on one of the leads; wires to offer the electrical connection between the other lead and LED's electrode; and sealing material such as transparent epoxy to seal the entire LED.
FIG. 1A is a plain view showing one example of the conventional SMD package type LED lamp. FIG. 1B is a cross sectional view cut along the line Y-Y in FIG. 1A.
As shown in FIG. 1A, an LED lamp 11 is structured such that the upper half region of an opening 12a in a package 12 of synthetic resin is provided with a single-sheet metal lead 13 extended from its left end to right end while being sandwiched within the package 12. On the lead 13, five LED's, two red LED's R1, R2 and two blue LED's B1, B2 and green LED G, are mounted in a line while having a narrow interval.
On the other hand, the lower half region of opening 12a is provided with a lead protrusion at nearly the center, and five leads 14a, 14b, 14c, 14d and 14e are sandwiched within the package 12 while being separated from the lead 13. These leads 13, 14a, . . . , 14e and the package 12 are integrally formed by disposing the leads 13, 14a, . . . , 14e in an injection mold for package 12 and then conducting the insert molding of package 12.
In the LED lamp 11, the leads 14a, . . . , 14e extended below the package are folded forward or backward along the lower surface of package 12. For example, the leads 14b, 14d are folded forward and the leads 14a, 14c and 14e are folded backward. The folded face is soldered to a mount board 18. Thus, the LED lamp 11 is mounted through solder 17 on the mount board 18.
Recently, an LED lamp to be used as a backlight for LCD of cellular phones having a rapidly increased demand, especially a field sequential type full-color LED lamp is needed to have a height of half or less the current height on the light emission surface side according as cellular phones are need to have a reduced thickness. In the LED lamp 11 as shown in FIG. 1A, where the five LED's are die bonded in the upper half region of light emission surface (opening 12a) and they are wire bonded to the leads 14a, . . . , 14e in the lower half region, it is impossible to further reduce the height on the light emission surface side.
On the other hand, the mounting workability of LED becomes serious according as the LED lamp is downsized. Namely, since the mounting area decreases as LED lamp is downsized, it is difficult to stably secure the electrical connection while securing a sufficient bonding strength.
Japanese patent application laid-open No. 2000-244022 discloses an LED lamp (herein referred to as prior art 1) that a recess to house a bump, solder ball, is provided at its bottom surface so as to enhance the bonding strength while using the bottom face and side face of recess as bonding surface.
FIG. 2 is a cross sectional view showing the LED lamp described in prior art 1. The LED lamp 30 is compose of an insulation board 31 and a thin plate 50 to be bonded through a adhesive film 40 to the insulation board 31.
The insulation board 31 is provided with a through-bore 31A to house an LED chip 32, and the through-bore 31A has first and second plating layers 54a, 54a on its bottom surface. The LED chip 32 is mounted on the first plating layer 54a and the upper-surface electrode of LED chip 32 is electrically connected through a wire 33 to the second plating layer 54a with a different polarity.
The thin plate 50 is formed by covering the lower surface of metal plates 51, 52 with insulative resin 53 while electrically insulating them at insulation part 53A. The thin plate 50 is also provided with a recess 50A to attach a bump 55 in its bottom surface. The recess 50 is covered with plating layers 54b, 54b and the bump 55 is attached therein. In this composition, when the bumps 55 is melted to conduct the solder bonding, the bottom face and side face of recess 50A being covered with the second plating layer 54b serve as a bonding surface. Therefore, the solder bonding property can be enhanced.
However, in the LED lamp disclosed in prior art, since the solder bonding property of LED lamp depends on the shape of solder, it is necessary to keep a constant bump shape to obtain a stable solder bonding property. Therefore, the manufacturing process must be complicated.